LOSS or WATER 



27 



32. External Anatomy of a Leaf. — We have seen 

 (Chapter II) that the three main parts of a leaf are the 

 blade, petiole and leaf-base. These parts may manifest 

 every conceivable variation as to shape and size, and bear 

 every relation to each other as to proportion. The petiole 



Fig. 17. — -Leaf of Hercules club {Aralia spinosa), partly thrice com- 

 pound. The leaf-blade measured 15 in. wide at the base, and 12 in. long. 

 (Photo by the author.) 



maybe more or less shortened, or it may be entirely wanting 

 so as to make the leaf-blade sessile (seated) on the stem (Figs. 

 14 and 15). The blade may be greatly enlarged (Fig. 16), 

 or more or less branched (Fig. 17), or it may be greatly re- 

 duced, or even entirely wanting. In the latler case, the 



